The present invention relates to nontoxic gas generating compositions that upon combustion-rapidly generate-gases that are useful for inflating occupant safety restraints in motor vehicles and specifically, the invention relates to thermally stable nonazide gas generants having not only acceptable burn rates, but that also, upon combustion, exhibit a relatively high gas volume to solid particulate ratio at acceptable flame temperatures.
The evolution from azide-based gas generants to nonazide gas generants is well-documented in the prior art. The advantages of nonazide gas generant compositions in comparison with azide gas generants have been extensively described in the patent literature, for example, U.S. Pat. Nos. 4,370,181; 4,909,549; 4,948,439; 5,084,118; 5,139,588 and 5,035,757, the discussions of which are hereby incorporated by reference.
In addition to a fuel constituent, pyrotechnic nonazide gas generants contain ingredients such as oxidizers to provide the required oxygen for rapid combustion and reduce the quantity of toxic gases generated, a catalyst to promote the conversion of toxic oxides of carbon and nitrogen to innocuous gases, and a slag forming constituent to cause the solid and liquid products formed during and immediately after combustion to agglomerate into filterable clinker-like particulates. Other optional additives, such as burning rate enhancers or ballistic modifiers and ignition aids, are used to control the ignitability and combustion properties of the gas generant.
One of the disadvantages of known nonazide gas generant compositions is the amount and physical nature of the solid residues formed during combustion. When employed in a vehicle occupant protection system, the solids produced as a result of combustion must be filtered and otherwise kept away from contact with the occupants of the vehicle. It is therefore highly desirable to develop compositions that produce a minimum of solid particulates while still providing adequate quantities of a nontoxic gas to inflate the safety device at a high rate.
The use of phase stabilized ammonium nitrate as an oxidizer, for example, is desirable because it generates abundant nontoxic gases and minimal solids upon combustion. To be useful, however, gas generants for automotive applications must be thermally stable when aged for 400 hours or more at 107 degrees C. The compositions must also retain structural integrity when cycled between −40 degrees C. and 107 degrees C. Further, gas generant compositions incorporating phase stabilized or pure ammonium nitrate sometimes exhibit poor thermal stability, and produce unacceptably high levels of toxic gases, CO and NOx for example, depending on the composition of the associated additives such as plasticizers and binders. Furthermore, recent revisions in U.S. car requirements require relatively minimal amounts of ammonia in the effluent gases.
Yet another problem that must be addressed is that the U.S. Department of Transportation (DOT) regulations require “cap testing” for gas generants. Because of the sensitivity to detonation of fuels known for their use in conjunction with ammonium nitrate, triaminoguanidine nitrate for example, many propellants incorporating ammonium nitrate do not pass the cap test unless shaped into large disks, which in turn reduces design flexibility of the inflator.
Yet another concern includes slower cold start ignitions of typical smokeless gas generant compositions, that is gas generant compositions that result in less than 10% of solid combustion products.
Yet another concern includes disposal and handling of organic compounds, solvents, and mixtures employed in the manufacture of polyvinyl(tetrazoles). The environmental impact associated with the use of organic solvents in the manufacture of polyvinyl(tetrazoles) includes related concerns of disposal, handling, and storage of these organic compounds. The flammability of many organic compounds increases the relative hazard of the manufacturing process, while the nature of the solvents requires storage and disposal in accordance with U.S.D.O.T. hazardous materials regulations.
Accordingly, ongoing efforts in the design of automotive gas generating systems, for example, include other initiatives that desirably produce more gas and less solids without the drawbacks mentioned above.
In yet another appropriate area, there has been an increasing need for versatile visual displays for electronic products of many kinds. Light-emitting diodes (“LEDs”) and liquid crystal displays (“LCDs”) have found many useful applications but have not been adequate in all cases. A visual display that is of relatively recent origin and that has shown much promise is the organic electroluminescent device. An electroluminescent device basically consists of an electroluminescent substance placed between a pair of electrodes. When an electric potential is applied across the electrodes, the electroluminescent substance emits visible light. Typically one of the electrodes is transparent, permitting the light to shine through.
Referring now to FIG. 8, an organic electroluminescent device known in the art includes an anode 401 on a substrate 403, a conducting polymer layer 405 adjacent the anode, a hole transport layer 407 adjacent the conducting polymer layer, an electron transport layer 409 adjacent the hole transport layer, and a cathode 411 adjacent the electron transport layer. When electric power is applied, biasing the anode positive with respect to the cathode, light is emitted at an interface 413 between the hole and electron transport layers.
FIG. 9 illustrates another typical electroluminescent device of the kind known in the art. A glass substrate 501, measuring perhaps 15 millimeters square, is coated with a transparent anode 503. A transparent hole transport layer 505 measuring about 10 millimeters square covers the anode and an electron transport layer 507 covers the hole transport layer, forming an interface 509 between the two layers. A cathode 511 covers the electron transport layer. In some devices the hole transport layer consists of two sublayers having slightly different composition, one sublayer forming a lower region 513 adjacent the anode and the other sublayer forming an upper region 515 adjacent the electron transport layer. The thicknesses of the anode, hole transport layer, electron transport layer and cathode are each of the order of 10-500 nanometers (100-5000 .Angstroms).
In operation, electric power from a voltage source 517 is applied to the anode and the cathode, biasing the anode positive with respect to the cathode. This causes regions of positive charge (“holes”) to migrate through the hole transport layer from the anode toward the electron transport layer and electrons to migrate from the cathode through the electron transport layer toward the hole transport layer. The holes and electrons combine at the interface 509 between the two layers, emitting visible light. The light propagates out of the device through the hole transport layer, the anode and the substrate as indicated by an arrow 519.
It would be a further advantage of the present invention, to simplify the manufacture of organic light emitting devices, and the complexity of the same.